1. Field of the Invention
The present invention relates to an oil circulating apparatus for an automatic transmission and more particularly to an oil circulating apparatus in which air jam noise can be reduced by supplying an oil containing a small number of bubbles to an oil pump.
2. Discussion of the Background Art
Generally, automatic transmission fluid (ATF) for operating and lubricating an automatic transmission including a multi-stage transmission and a continuously variable transmission, is reserved in an oil reservoir such as oil pan and the like provided under the automatic transmission. The automatic transmission fluid reserved in the oil pan is sucked up by an oil pump through an oil strainer and supplied to a torque converter, miscellaneous lubrication parts, a hydraulic servo mechanism and the like, after being regulated to a specified pressure in a hydraulic circuit. The automatic transmission fluid discharged from the servo mechanism and the lubrication parts is returned directly to the oil reservoir and the automatic transmission fluid (hereinafter, referred to as ATF) discharged from the torque converter is circulated to the oil reservoir after being cooled by an oil cooler.
In the automatic transmission, since the ATF is agitated by miscellaneous rotation members such as a planetary gear set, a final gear set, miscellaneous friction devices, a belt type driving force transmitting mechanism and the like, the ATF is returned to the oil reservoir while many bubbles are contained therein and the ATF containing bubbles is sucked up by the oil pump. As a result, an air jam noise is generated from the oil pump.
Japanese Patent Application Laid-open No. Toku-Kai-Hei 11-22811 proposes a technique for reducing the number of bubbles contained in oil when oil is sucked up by an oil pump. Specifically, in this disclosure, a guiding means provided in an oil pan first guides stream of lubricating oil in an opposite direction to an inlet of an oil strainer, reduces the flow speed of oil, breaks wave, stabilizes an oil level and finally introduces lubricating oil containing a small number of bubbles to the inlet of the oil strainer.
Further, Japanese Patent Application Laid-open No. Toku-Kai-Hei 8-246835 discloses a technique in which a protruding portion is provided on a relief valve side of an oil strainer, a suction port of an oil strainer is disposed on a side of the protruding portion and at a higher position than the protruding portion so as to prevent the lubricating oil gushed out of the relief valve from coming into the suction port of the oil strainer together with bubbles.
However, according to the technique disclosed in Toku-Kai-Hei 11-22811, the stream of lubricating oil discharged from the oil cooler to the oil pan is once guided in the opposite direction to the inlet port of the oil strainer, however, it is difficult to remove bubbles contained in lubricating oil completely and therefore it is impossible to suppress the generation of the air jam noise.
On the other hand, according to the technique disclosed in Toku-Kai-Hei 8-246835, although the oil discharged from the relief valve can be prevented from the mixing-in of bubbles, in case where bubbles mix in lubricating oil as a result of the agitation by rotating members of the automatic transmission, it is also impossible to prevent the mixing-in of bubbles completely and therefore the generation of air jam noise can not be suppressed.
It is an object of the present invention to provide an oil circulating apparatus of an automatic transmission capable of suppressing the generation of air jam noise from the oil pump.
An oil circulating apparatus of an automatic transmission comprises an oil passage provided downstream of an oil cooler, an oil strainer provided in an oil reservoir and connected with the suction side of the oil pump, a discharge port of the oil passage provided at an downstream end of the oil passage and an suction port of the oil strainer provided opposite and adjacent to the discharge port.